The water regulator is taking action against four more water companies, including Severn Trent and United Utilities, meaning every wastewater company in England and Wales is under investigation over sewage spills.

Ofwat said it had served formal notices on Dŵr Cymru Welsh Water, Hafren Dyfrdwy, Severn Trent and United Utilities, asking them to provide evidence for its investigation into companies’ wastewater management in England and Wales.

The regulator has looked at the companies’ environmental performance and data about how often they spill from storm overflows. It said this had heightened its “concerns that these companies may not be fulfilling their obligations to protect the environment and minimise pollution”.